PDF Extraction using PDFgetx2

[Ritesh Uppuluri]

Hello everyone,

This is Ritesh Uppuluri, a postdoc at Argonne National Laboratory. I am currently analyzing PDF data obtained on lithiated silicon anodes collected at 11-ID-B beamline at APS.  I am currently figuring out the best approach to subtract the background from my system. I tried the following approaches to extract PDF using PDFgetx2 software:

1. In the first approach, I used the Kapton holder as the background to be subtracted from the sample. The S(Q) data seemed reasonable but oscillates beyond 13 A-1.  So, I extracted G(r) using a Qmax of 13 A-1 (see attached plots).

2. In the second approach, I tried subtracting other background components present in my anode, such as carbon black and binder, in addition to Kapton. This is to eliminate effects from these components on G(r). Using this approach, I see that part of the S(Q) data is buried under the baseline. When I extract G(r) using this approach, it looks a little different from what I got using the first approach above.

Can someone advice me on the best approach to use to get meaningful G(r) data for this system that minimizes interference from the background components? I have attached snippets of my plots using both approaches. I am looking for subtle changes in the structure by incorporation of other metals from the electrolyte. So, it would be best to eliminate correlations from background aside from phases of interest. I appreciate your help.

Thanks,

Ritesh

[Simon Billinge]

Hi Ritesh,

In our group we would use PDFgetX3 (not getX2) for this and would probably subtract the empty carbon from the loaded carbon samples.

S

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Simon Billinge

Professor, Columbia University

Physicist, Brookhaven National Laboratory

[Ritesh Uppuluri]

Thanks Simon. I will look into PDFgetx3. By subtracting empty carbon, do you mean just carbon without other background components (e.g. binder)? Or carbon without the Kapton holder?

Ritesh

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Ritesh Uppuluri

Graduate Student, Department of Chemistry

Mallouk Research Group

The Pennsylvania State University, University Park, PA

[Ritesh Uppuluri]

Hello everyone,

While I am still trying to learn PDFgetx3 for PDF extraction, I had a question about refinement using PDFgui.  I tried modeling PDF data for pure Silicon (see attached) and I think I am getting an okay fit but the refinement is poorer at low r-regions (due to the wiggles). The residual is still pretty high at 0.463. I attempted  a refinement by varying the lattice parameters (5.43204), scale factor (1.125), the displacement parameters (0.01137), quadratic atomic correlation factor (5.1596), Qdamp (0.08261) and Qbroad (0.00115). Values in parentheses are refined values obtained by refinement against Si diamond structure. Are the refined values reasonable? Can we improve this fit further? I used a fit range of 0.5-30 Angstroms for my refinement. I am not sure if something is wrong with the extraction process as well.   

I appreciate your help.

Thanks,

Ritesh

[Simon Billinge]

Hi Ritesh,

The problem is the quality of your experimental PDF.  For something like Si we get much lower wiggles and can get Rw below 0.04 or so.

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[Hansen, Anna-Lena (IAM)]

Dear Ritesh,

have you subtracted the empty capillary? To me it looks like you still have the contribution of an amorphous phase.

All the best

Anna

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[Ritesh Uppuluri]

Hi Anna,

Yes, the data was extracted after background subtraction from the capillary (Kapton).

Ritesh

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